11:00 〜 13:00
[MIS18-P05] The response of coral reef development to climate conditions on Holocene uplifted terraces in Kikai Island, Japan
キーワード：coral reef, coral carbonate production, oxygen isotopes, Holocene, the East Asian monsoon, Kikai Island
The decline of coral reefs has been concerned about recent climate change and sea-level rise. However, the relationship between climate conditions and coral reef development is still unknown. In this study, we reconstructed the composition of coral communities, coral carbonate production, and climate condition (sea surface temperature and salinity) from Holocene uplifted terraces in Kikai Island, Japan, and discussed the relationship between reef growth and climate change during mid to late Holocene.
Kikai Island is located at the central Ryukyus, the subtropical and temperate area boundary, and the border between the East China Sea and the Pacific Ocean. Kikai Island's coast is composed of four terraces (Terrace Ⅰ - Ⅳ) developed from 8.1 ka to 1.4 ka. The topographic profiles and coral genus composition along five transects crossed over from Terrace Ⅱ to Ⅳ (Ⅱ; 6.3-4.1 ka, Ⅲ; ~3.1ka, Ⅳ; ~1.4 ka) around the island. Coral carbonate production (CCP) in each terrace was calculated from each coral genus's coverage, skeletal density, and growth rate. Seasonal variation of SST and salinity were reconstructed by oxygen isotopes and strontium/calcium ratios in fossil Porites corals skeletons from each terrace.
The group of coral genera was classified by its tropical and temperate adapted type in modern Japanese areas. The coverage of tropical adapted corals, including Acropora sp., was small on terrace Ⅲ on the east coast and vice versa on the west coast. The temperate adapted corals were increased with decreasing the tropical adapted corals, especially on terrace Ⅲ. CCP values were generally correlated with the cover of Acropora sp. The seasonal variation of reconstructed SST and salinity through Holocene suggested the strength of the East Asian monsoon.
These results revealed the relationship between climate and coral reef developments in Kikai Island. Terrace Ⅱ was highly developed under a warm (Holocene climatic optimum) climate and strong summer monsoon conditions. On terrace Ⅲ on the east coast, cooling weather decreased the abundance of tropical adapted corals and CCP. However, coral diversity was increased with a lot of temperate adapted corals. On terrace Ⅲ at the west coast, strong winter monsoon (northwest wind) developed coral reef. On terrace Ⅳ, the cover of Acropora sp. and CCP was recovered to transition to a modern, warm climate. Reef corals changed their diversity and have kept the reef growth through the Holocene in Kikai Island.
Kikai Island is located at the central Ryukyus, the subtropical and temperate area boundary, and the border between the East China Sea and the Pacific Ocean. Kikai Island's coast is composed of four terraces (Terrace Ⅰ - Ⅳ) developed from 8.1 ka to 1.4 ka. The topographic profiles and coral genus composition along five transects crossed over from Terrace Ⅱ to Ⅳ (Ⅱ; 6.3-4.1 ka, Ⅲ; ~3.1ka, Ⅳ; ~1.4 ka) around the island. Coral carbonate production (CCP) in each terrace was calculated from each coral genus's coverage, skeletal density, and growth rate. Seasonal variation of SST and salinity were reconstructed by oxygen isotopes and strontium/calcium ratios in fossil Porites corals skeletons from each terrace.
The group of coral genera was classified by its tropical and temperate adapted type in modern Japanese areas. The coverage of tropical adapted corals, including Acropora sp., was small on terrace Ⅲ on the east coast and vice versa on the west coast. The temperate adapted corals were increased with decreasing the tropical adapted corals, especially on terrace Ⅲ. CCP values were generally correlated with the cover of Acropora sp. The seasonal variation of reconstructed SST and salinity through Holocene suggested the strength of the East Asian monsoon.
These results revealed the relationship between climate and coral reef developments in Kikai Island. Terrace Ⅱ was highly developed under a warm (Holocene climatic optimum) climate and strong summer monsoon conditions. On terrace Ⅲ on the east coast, cooling weather decreased the abundance of tropical adapted corals and CCP. However, coral diversity was increased with a lot of temperate adapted corals. On terrace Ⅲ at the west coast, strong winter monsoon (northwest wind) developed coral reef. On terrace Ⅳ, the cover of Acropora sp. and CCP was recovered to transition to a modern, warm climate. Reef corals changed their diversity and have kept the reef growth through the Holocene in Kikai Island.